PSI - Issue 19

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Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000 – 000 Structural Integrity Procedia 00 (2019) 000 – 000

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Procedia Structural Integrity 19 (2019) 294–301

Fatigue Design 2019 Effect of Surface Roughness on Fatigue Strength of Ti-6Al-4V Alloy Manufactured by Additive Manufacturing Masanori Nakatani a, *, Hiroshige Masuo b , Yuzo Tanaka a , Yukitaka Murakami a,c a Kobe Material Testing Laboratory Co. Ltd., Harima-Town, Hyogo 675-0135, Japan b Metal Technology Co. Ltd., Ebina, Kanagawa, 243-0424, Japan c Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan This study focuses on the effects of surface roughness on the fatigue strength of Ti-6Al-4V alloy manufactured by additive manufacturing (AM); electron beam melting (EBM) and direct metal laser sintering (DMLS) methods. The hot isostatic pressing (HIP) was applied to some series of polished specimens and as-built specimens to eliminate internal defects. Fatigue limit was evaluated by rotating bending fatigue tests. Although HIP increased the fatigue limits slightly, the fatigue limits of as-built specimens with HIP were only about 30% of the ideal fatigue limit expected from the Vickers hardness. On the other hand, the polished specimens with HIP had the fatigue limit close to the ideal upper bound. The fatigue crack was initiated at multiple sites on the surface in as-built specimens. Thus, surface roughness has crucial influence on fatigue strength of AM component. The surface morphology of as-build specimen is three-dimensionally complex. The evaluation of equivalent defect size for surface roughness was attempt by √area parameter model assuming the surface roughness is a small defect. The estimated defect size was over the applicable range of the √area parameter model, suggesting that the surface roughness of as -built specimen should be considered as long crack. Fatigue Design 2019 Effect of Surface Roughness on Fatigue Strength of Ti-6Al-4V Alloy Manufactured by Additive Manufacturing Masanori Nakatani a, *, Hiroshige Masuo b , Yuzo Tanaka a , Yukitaka Murakami a,c a Kobe Material Testing Laboratory Co. Ltd., H rima-Town, Hyogo 675-0135, Japan b Metal Technology Co. Ltd., Ebina, Kanagawa, 243-0424, Japan c Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan Abstract This study focuses on the effects of surface roughness on the fatigue stre gth of Ti-6Al-4V alloy manufactured by additive manufacturing (AM); electron beam melting (EBM) and direct metal las r sintering (DMLS) methods. Th hot isostatic pressing (HIP) was applied to some series of polished specimens and as-built specimens to eliminate internal defects. Fatigue limit was evaluat d by rotating bending fatigue tests. Although HIP increased the fatigue limits slightly, the fatigue limits of as-built specimens with HIP were only about 30% of the ideal fatigue limit expected from the Vickers hardness. On the other hand, the polished specimens with HIP had the fatigue limit close to the ideal upper bound. The fatigue crack was initiated at multiple sites on the surface in as-built specimens. Thus, surface roughness has crucial influence on fatigue strength of AM component. Th surface morphology of as-build specimen is three-di e sionally complex. The evaluation of quivalent defect size for surface roughn ss was ttempt by √area parameter model assuming the surface roughness is a small defect. The estimat d defect size was over the applicable r nge of the √area parameter model, suggesting that the surface roughness of as -built specimen should be considered as long crack. Abstract

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers.

Keywords: Additive manufacturing, Fatigue, Surface roughness, Titanium alloy, Hot isostatic pressing, √area parameter model , Keywords: Additive manufacturing, Fatigue, Surface roughness, Titanium alloy, Hot isostatic pressing, √area parameter model ,

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. * Correspon ing author. Tel.: +81-79-435-5010; fax: +81-79-435-5102. E-mail address: ma-nakatani@kmtl.co.jp * Corresponding author. Tel.: +81-79-435-5010; fax: +81-79-435-5102. E-mail address: ma-nakatani@kmtl.co.jp

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 10.1016/j.prostr.2019.12.032